When he can't get enough of you (and won't leave you alone), when he can't do enough for you/your friends/your neighbours (but it's actually all about polishing his halo), when he seems too good to be true (and he isn't true, a lot of it is lies), when he's had a tough time (because he's always the victim, never the perpetrator), and his ex is a crazy woman (of course she is, and you'll be the next one). Any of these are bad on their own, but in combination they're really not good.
But even though there may be enough flags to make bunting, some abusers are so good they can keep the mask going for a decade or more until you suddenly realise you're a frog and the water is near boiling...
The best thing you can do, as a friend, is to be there for when she realises that she's in an abusive relationship...and help her to get out of it. If you want to use your SM to highlight stuff, by all means go ahead, but don't be surprised if it doesn't even occur to her that it's relevant to her; I remember blithely telling a midwife that I was shocked they had to ask about DV, because "D"H would never do anything like that...a month later, after the baby was born, he did.
FWIW, most of my friends saw the charm and if they registered some of the occasional "off" stuff, like me they put it down to him having a bad day. Looking back his mask slipped - briefly - so many times, but none of us worked it out because it seemed so out-of-character; it's only now, looking back, that I, and they can see it. Sadly abuse is a lot easier to see in hindsight.